Heretofore it has been standard procedure for lithographic printing presses to use dampening fluid which preferably comprises a mixture of water and water soluble, volatile, organic liquid such as alcohol, esters, ketones and similar compounds which are compatible with, and receptive to, oil-based ink. Commercial grade isopropyl alcohol is preferably employed because of its economy and ready availability. Such material is molecularly compatible with ink because the vehicle of the ink is organic material and the dampening fluid containing alcohol is organic material.
It has been found that mixing 10 to 25% alcohol with water works satisfactorily for most lithographic printing operations. Dampening fluid containing alcohol is quickly absorbed in the inking system because it is ink compatible and rides on and into the surface of ink coated form rollers in a uniformly thin layer and evaporates quickly. Upon evaporation, alcohol does not cause oxidation as does water and, furthermore, it provides a cooling agent for the rollers running in contact. There are numerous other important reasons for using alcohol.
Recently, concern has developed that evaporation of alcohol may damage the environment. However, if alcohol is not mixed with the dampening fluid, then "ridging" occurs whereby water rings are formed on the chrome roller resulting in unwanted lines and "ghosting" on the final printed sheets.
"Ghosting" is the variation in the color of the printed image on the sheet resulting from an improper ink-water balance on the surface of the printing plate. An improper ink-water balance may result from the accumulation of excess ink in streaks on inker form rollers in areas corresponding to non-image areas on the printing plate. A similar phenomena results when "water streaks" in a non-uniform film of dampening fluid on the chrome roller are transferred to the dampener form roller which causes "ridging" or streaking on the plate and the printed sheet.